In a cellular orthogonal frequency division multiplexing (OFDM) wireless packet communication system, uplink/downlink data packet transmission is performed on a subframe basis and one subframe is defined by a certain time interval including a plurality of orthogonal frequency division multiplexing (OFDM) symbols.
3rd Generation Partnership Project Long Term Evolution (3GPP LTE) supports a type 1 radio frame structure applicable to frequency division duplex (FDD), and a type 2 radio frame structure applicable to time division duplex (TDD). For convenience of description, the term “radio frame” will be referred to as a frame. The structure of a type 1 radio frame is shown in FIG. 1. The type 1 radio frame includes 10 subframes, each of which consists of two slots. The structure of a type 2 radio frame is shown in FIG. 2. The type 2 radio frame includes two half-frames, each of which is made up of five subframes, a downlink piloting time slot (DwPTS), a guard period (GP), and an uplink piloting time slot (UpPTS), in which one subframe consists of two slots. That is, one subframe is composed of two slots irrespective of the radio frame type.
In the 3GPP LTE system, a signal transmitted from each downlink slot can be described by a resource grid including NRBDL NSCRB and NsymbDL OFDM symbols. Here, NRBDL represents the number of resource blocks (RBs) in a downlink, NSCRB represents the number of subcarriers constituting one RB, and NsymbDL represents the number of OFDM symbols in one downlink slot. The structure of this resource grid is shown in FIG. 3.
In the 3GPP LTE system, a signal transmitted from each uplink slot can be described by a resource grid including NRBUL NSCRB subcarriers and NsymbDL Single Carrier—Frequency Division Multiple Access (SC-FDMA) symbols. Here, NRBUL represents the number of resource blocks (RBs) in an uplink, NSCRB represents the number of subcarriers constituting one RB, and NsymbUL represents the number of SC-FDMA symbols in one uplink slot. The structure of this resource grid is shown in FIG. 4.
Each element contained in the resource grid is called a resource element, and can be identified by an index pair (k,l) contained in a slot, where k is an index in a frequency domain, and l is an index in a time domain.
RBs may be used to describe a mapping relationship between physical channels and resource elements. The RBs may be differently defined in a physical region and a logical region. In this definition of RBs, the RBs can be divided into physical resource blocks (PRBs) in the physical region and virtual resource blocks (VRBs) in the logical or virtual region. The PRBs may be referred to as physical resource units (PRUs), and the VRBs may be referred to as logical resource units (LRUs). One PRB may be mapped to one VRB. A mapping relationship between the VRBs and the PRBs can be described on a subframe basis. In more detail, this mapping relationship can be described in units of each of slots constituting one subframe. Also, the mapping relationship between the VRBs and the PRBs can be described using a mapping relationship between indexes of the VRBs and indexes of PRBs. A detailed description of this will be further given in embodiments of the present invention. A PRB is defined by NsymbDL consecutive OFDM symbols in a time domain and NSCRB consecutive subcarriers in a frequency domain. One PRB is therefore composed of NsymbDL NSCRB resource elements. The PRBs are assigned numbers from 0 to NRBDL−1 in the frequency domain.
A VRB can have the same size as that of the PRB. There are two types of VRBs defined, the first one being a localized type and the second one being a distributed type. For each VRB type, a pair of VRBs have a single VRB index (which may hereinafter be referred to as a ‘VRB number’) and are allocated over two slots of one subframe. In other words, NRBDL VRBs belonging to a first one of two slots constituting one subframe are each assigned any one index of 0 to NRBDL−1, and NRBDL VRBs belonging to a second one of the two slots are likewise each assigned any one index of 0 to NRBDL−1.
The index of a VRB corresponding to a specific virtual subcarrier of the first slot has the same value as that of the index of a VRB corresponding to the specific virtual subcarrier of the second slot. That is, assuming that a VRB corresponding to an ith virtual subcarrier of the first slot is denoted by VRB1(i), a VRB corresponding to a jth virtual subcarrier of the second slot is denoted by VRB2(j) and index numbers of the VRB1(i) and VRB2(j) are denoted by index(VRB1(i)) and index(VRB2(j)), respectively, a relationship of index(VRB1(k))=index(VRB2(k)) is established (see FIG. 5(a)).
Likewise, the index of a PRB corresponding to a specific physical subcarrier of the first slot has the same value as that of the index of a PRB corresponding to the specific physical subcarrier of the second slot. That is, assuming that a PRB corresponding to an ith physical subcarrier of the first slot is denoted by PRB1(i), a PRB corresponding to a jth physical subcarrier of the second slot is denoted by PRB2(j) and index numbers of the PRB1(i) and PRB2(j) are denoted by index(PRB1(i)) and index(PRB2(j)), respectively, a relationship of index(PRB1(k))=index(PRB2(k)) is established (see FIG. 5(b)).
Some of the aforementioned VRBs are allocated as the localized type and the others are allocated as the distributed type. Hereinafter, the VRBs allocated as the localized type will be referred to as ‘localized virtual resource blocks (LVRBs)’ and the VRBs allocated as the distributed type will be referred to as ‘distributed virtual resource blocks (DVRBs)’.
The LVRB of index i corresponds to the PRB of index i. That is, an LVRB1 having the index i corresponds to a PRB1 having the index i, and an LVRB2 having the index i corresponds to a PRB2 having the index i (see FIG. 6). In this case, it is assumed that the VRBs of FIG. 6 are all allocated as LVRBs.
However, the distributed VRBs (DVRBs) may not be directly mapped to PRBs. That is, the indexes of the DVRBs can be mapped to the PRBs after being subjected to a series of processes.
First, the order of a sequence of consecutive indexes of the DVRBs can be interleaved by a block interleaver. Here, the sequence of consecutive indexes means that the index number is sequentially incremented by one beginning with 0. A sequence of indexes output from the block interleaver is sequentially mapped to a sequence of consecutive indexes of PRB1s (see FIG. 7). It is assumed that the VRBs of FIG. 7 are all allocated as DVRBs. On the other hand, the sequence of indexes output from the block interleaver is cyclically shifted by a predetermined number and the cyclically shifted index sequence is sequentially mapped to a sequence of consecutive indexes of PRB2s (see FIG. 8). It is assumed that the VRBs of FIG. 7 or FIG. 8 are all allocated as DVRBs. In this manner, PRB indexes and DVRB indexes can be mapped over two slots.
In this case, the block interleaver shown in FIG. 7 or in FIG. 8 may be omitted.
According to the above-mentioned processes of mapping DVBRs to PRBs, a PRB(i) and a PRB2(j) having the same index i can be mapped to a DVRB1(m) and a DVRB2(n) having different indexes m and n. For example, referring to FIG. 7 and FIG. 8, a PRB1(1) and a PRB2(1) are mapped to a DVRB1(6) and a DVRB2(9) having different indexes. A frequency diversity effect can be obtained based on this DVRB mapping scheme.
A variety of methods for allocating such VRBs may be used, for example, a bitmap method and a compact method. According to the bitmap method, resources can be freely allocated throughout the system band, and non-consecutive RBs can also be allocated. However, the above-mentioned bitmap method has a disadvantage in that it unavoidably increases the number of bits requested for allocation of RBs as the number of the RBs increases. According to the compact method, only one set of consecutive RBs can be assigned throughout the system band. In order to represent the consecutive RBs, a resource indication value (RIV) may be defined. This RIV may represent a combination of a start point (S) of the series of allocated RBs among all RBs and a length (L) of the series of allocated RBs. According to the number of generable combinations of the start point (S) and the length (L), the number of bits representing a certain RIV for indicating a specific combination is decided by the above compact method. Assuming that the number of bits representing this RIV can be reduced, the remaining bits may be used to transmit other information.